Currently, on an international scale, ultrasound breast examination is an accepted medical modality applied both as a primary method for evaluation of the breasts of young patients, that is, those under 40 years of age, and as an adjunct to x-ray mammography. See, for example, Kasumi, F., et al., “Topics in Breast Ultrasound,” Seventh International Congress on the Ultrasonic Examination of the Breast, Shinohara Publications, Inc., 1-7, Hongo 2-chome, Bunkyo-ku, Tokyo 113, Japan, 1991; Tohno, E., et al., Ultrasound Diagnosis of Breast Diseases, New York, Churchill-Livingstone, 1994; and, Stavros, A. T., et al., “Solid Breast Nodules: Use of Sonography to Distinguish Between Benign and Malignant Lesions,” Radiology 196, pp. 123-134, 1995. In terms of the diagnostic effectiveness of the ultrasound breast imaging, a number of investigators from the early 1980s to the present have shown that this modality is not limited to diagnosing the solid or cystic nature of a breast mass. It is capable, with a high degree of accuracy, of providing imaging data which permits differentiation of benign and malignant breast masses. See, for example, Stavros, A. T., et al., “Solid Breast Nodules: Use of Sonography to Distinguish Between Benign and Malignant Lesions,” Radiology 196, pp. 123-134, 1995; Kelly-Fry, E., et al., “Factors Critical to Highly Accurate Diagnosis of Malignant Breast Pathologies by Ultrasound Imaging,” Ultrasound 82, eds., Lerski, R. A., et al., Pergamon Press, Oxford and New York, 1983; Harper, P., et al., “Breast Ultrasound: Report of a 5-Year Combined Clinical and Research Program,” Le Journal Francais d'Echographie, 2n 5, pp. 133-139, 1984; Ueno, E., et al., “Classification and Diagnostic Criteria in Breast Echography,” Japan Journal of Medicine, Ultrasonics, vol. 13, no. 1, pp. 19-31, 1986 (in English); Ueno, E., et al., “Dynamic Tests in Real-Time Breast Echography,” Ultrasound in Med. & Biology, 14 (supp. 1), pp. 53-57, 1988; Tohnosu, N., et al., “Clinical Evaluation of Ultrasound in Breast Cancers in Comparison with Mammography, Computed Tomography and Digital Subtraction Angiography,” Topics in Breast Ultrasound, eds., Kasumi, F., et al., Shinohara Pub. Inc., Tokyo, Japan, 1991; and, Gerlach, B., et al., “Comparison of X-ray Mammography and Sonomammography of 1,209 Histological Verified Breast Diseases,” Breast Ultrasound Update, eds., Madjar, H., et al., Karger, Basel, Freiburg, N.Y., 1994. In Japan, ultrasound breast imaging has equal diagnostic status with x-ray mammography. See, for example, Ueno, E., et al., “Classification and Diagnostic Criteria in Breast Echography,” Japan Journal of Medicine, Ultrasonics, vol. 13, no. 1, pp. 19-31, 1986 (in English); Ueno, E., et al., “Dynamic Tests in Real-Time Breast Echography,” Ultrasound in Med. & Biology, 14 (supp. 1), pp. 53-57, 1988; Tohnosu, N., et al., “Clinical Evaluation of Ultrasound in Breast Cancers in Comparison with Mammography, Computed Tomography and Digital Subtraction Angiography,” Topics in Breast Ultrasound, eds., Kasumi, F., et al., Shinohara Pub. Inc., Tokyo, Japan, 1991. European investigators have found that ultrasound breast imaging can equal the accuracy of x-ray mammography in the diagnosis of overt, malignant breast masses. See, for example, Gerlach, B., et al., “Comparison of X-ray Mammography and Sonomammography of 1,209 Histologically Verified Breast Diseases,” Breast Ultrasound Update, eds., Madjar, H., et al., Karger, Basel, Freiburg, N.Y., 1994; Dambrosio, F., et al., “Clinical Program of Breast Surveillance by Means of Echopalpation: Results from January 1985 to May 1992,” Breast Ultrasound Update, eds., Madjar, H., et al., Karger, Basel, Freiburg, N.Y., 1994; and, Leucht, W., et al., “Is Breast Sonography an Additional Method for the Diagnosis of Palpable Masses,” Topics in Breast Ultrasound, eds., Kasumi, F., et al., Shinohara Pub. Inc., 11-7 Hongo 2-chome, Bunkyo-ku, Tokyo 113, Japan, 1991. In the United States, many clinicians during the 1980s and early 1990s restricted ultrasound breast imaging to a limited role of differentiation between cystic and solid masses. See, for example, Sickles, E. A., “Imaging Techniques Other Than Mammography for the Detection and Diagnosis of Breast Cancer,” Recent Results in Cancer Research, 119, pp. 127-135, 1990; Jackson, V. P., “The Role of US in Breast Imaging,” Radiology, 177, pp. 305-311, 1990; Bassett, L. W., et al., “Breast Sonography,” American Journal of Radiology, 156 (3), pp. 449-455, 1991; Feig, S. A., “Breast Masses: Mammographic and Sonographic Evaluation,” Radiol. Clin. North Am., 30, pp. 67-93, 1992; and, Orel, S. G., et al., “Nonmammographic Imaging of the Breast: Current Issues and Future Prospects,” Sem. In Roentgenology, XXVIII, no. 3, pp. 231-241, 1993. Following the 1995 publication of a clinical study which provided further data on the successful differentiation of benign and malignant masses by ultrasound breast imaging techniques, this modality was more widely applied in the United States. See, for example, Stavros, A. T., et al., “Solid Breast Nodules: Use of Sonography to Distinguish Between Benign and Malignant Lesions,” Radiology 196, pp. 123-134, 1995.
Since the 1980s, most ultrasound breast examinations have been carried out with the patient in the supine position. Imaging is carried out by moving a handheld ultrasound transducer across the free flowing surface of the breast and recording the images on film. By contrast, for x-ray mammography, the patient is in a standing or sitting position with the breast compressed between a plastic paddle and the surface of an x-ray film holder module. The breast is alternately compressed in various orientations such as cranio-caudal, lateral and oblique while the x-ray beam traverses the breast in each of these positions. For each individual position, an image is recorded. Currently, to correlate precisely standard breast ultrasound imaging data with that provided by x-ray mammography data can sometimes be impossible because the anatomical orientations of tissues traversed by the x-ray beam for the various compressed breast positions are different from the anatomical position of tissues traversed by the ultrasound beam following its entrance into an uncompressed breast in a supine position. Also, since tissue is mobile, the location of a breast mass as imaged when a breast is compressed between two plates can be different from that of its imaged location when the breast is uncompressed and in a supine position. These problems can lead to diagnostic errors.
In an attempt to improve correlation between ultrasound and x-ray imaging data, in 1983 Novak demonstrated a technique for holding the breast in the same positions used in x-ray mammography while applying a linear array ultrasound transducer in direct contact with the breast surface. See, Novak, D., “Indications for and Comparative Diagnostic Value of Combined Ultrasound and X-ray Mammography,” European Journal of Radiology, 3, 1983. A plexiglas plate was used as a support on one side of the breast while the ultrasound transducer contacted the skin surface of the opposite side. The breast was not compressed between two plates.
In the early 1990s, Kelly-Fry, et al., demonstrated that specially designed breast compression paddles, constructed from various types and thicknesses of plastics, including polyesters, polycarbonates and acrylics, can transfer both x-ray and ultrasound, without serious attenuation of either modality. See, for example: Kelly-Fry, E., et al., “A New Ultrasound Mammography Technique That Provides Improved Correlation With X-ray Mammography,” Amer. Col. Radiol., 24th National Conference on Breast Cancer, New Orleans, La., March 1990; Kelly-Fry, E., et al., “Adaptation, Development and Expansion of X-ray Mammography Techniques for Ultrasound Mammography,” Journal of Ultrasound in Medicine, 10, no. 3, S 16, supplement, March 1991; Kelly-Fry, E., “New Techniques for Ultrasound Mammography,” National Cancer Institute Breast Imaging Workshop, Bethesda, Md., Sep. 4-6, 1991; and, Kelly-Fry, E., et al., “Rapid Ultrasound Scanning of Both Breasts Positioned and Compressed in the Mode of X-ray Mammography,” Journal of Ultrasound in Medicine, 13, no. 3, S41-42 supplement, March, 1994. Instrumentation systems which incorporated these compression paddles were designed and applied to patients with the purpose of ultrasonically imaging a breast while it was held under the same compression and position orientations used in x-ray mammography. A hand-held ultrasound linear array transducer placed in contact with the compression plate was used for imaging.
Subsequent investigations of this approach by Dines, et al., Romilly-Harper, et al., and Kelly-Fry, et al., included automation of the transducer motion, use of high ultrasound frequencies, such as, for example, 7.5 MHz, 10 MHz and 13 MHz, 3D ultrasound imaging and clinical application of the system. See, for example, Dines, K. A., et al., “Automated Three-Dimensional Ultrasound Breast Scanning in the Craniocaudal Mammography Position,” Ninth International Congress on the Ultrasonic Examination of the Breast, Sep. 28-Oct. 1, 1995, pp. 43-44; Dines, K. A., et al., “Automated Three-Dimensional Ultrasonic Breast Scanning in the Compressed Mammography Position,” Journal of Ultrasound in Medicine, vol. 18, no. 3, supplement, March, 1999; Romilly-Harper, A. P., et al., “Clinical Evaluation of Manual, Automated and 3-D Ultrasound Imaging of Breasts Compressed in the Same Position Modes Applied in X-ray Mammography,” Ninth International Congress on the Ultrasonic Examination of the Breast, Sep. 28-Oct. 1, 1995, pp. 45-46; and, Kelly-Fry, E., et al., “Mammography Instrumentation for Combined X-ray and Ultrasound Imaging,” Ninth International Congress on the Ultrasonic Examination of the Breast, Sep. 28-Oct. 1, 1995.
To obtain data on the ultrasound attenuation and velocity of breast tumors, Richter designed a system in which a breast is compressed between two thick, for example, approximately 0.39 inch (10 mm), plexiglas plates, in the craniocaudal position. A metal reflector is placed on the inferior plexiglas plate and a linear array transducer is in contact with the upper plate. See, for example, Richter, K., “Technique for Detecting and Evaluating Breast Lesions,” Journal of Ultrasound in Medicine, 13, pp. 797-802, 1994 and Richter, K. “Detection of Diffuse Breast Cancers with a New Sonographic Method,” J. Clin. Ultrasound, 24, pp. 157-168, May, 1996. No x-ray imaging system was included in this initial instrumentation. The thick plexiglas compression paddle was inappropriate for x-ray breast imaging because of its increased attenuation of the x-ray beam. See, for example, Kelly-Fry, E., et al., “Mammography Instrumentation for Combined X-ray and Ultrasound Imaging,” Ninth International Congress on the Ultrasonic Examination of the Breast, Sep. 28-Oct. 1, 1995. The thickness of the compression plate was also inappropriate for ultrasound imaging, causing increased ultrasound attenuation and multiple artifactual reflections within the breast image. In subsequent investigations, Richter, et al., carried out clinical studies at a low frequency, 5 MHz, using automated transducer motion with attachment of the imaging system to a standard x-ray unit. See, for example, Richter, et al., “Description and First Clinical Use of a New System for Combined Mammography and Automated Clinical Amplitude/Velocity Reconstructive Imaging (CARI) Breast Sonography, Invest. Radiol., 32, pp. 19-28, 1997, Richter, K., et al., “Detection of Malignant and Benign Breast Lesions with an Automated US System: Results in 120 Cases,” Radiology, 205, pp. 823-830, 1997; 5,603,326; and, 5,840,022.
Other patents illustrate and describe instrument systems which combine x-ray mammography and ultrasound mammography using breast compression materials that are radiolucent and sonolucent. See, for example, U.S. Pat. Nos. 5,474,072; 5,479,927; and WO 95/11627. Earlier publications on the development and application of a combined x-ray and ultrasound mammography system using breast compression paddles that transmit both x-rays and ultrasound are not referenced. A breast examination system based upon these references was commercially marketed as a 3D ultrasound-guided breast biopsy system.
U.S. Pat. No. 5,776,062 illustrates and describes a system for applying x-rays to identify a region in a breast containing a possible malignant mass. Subsequently, ultrasound imaging is performed in order to target the x-ray identified region. Ultrasound-guided biopsy is then based on the combined data. The system is not designed for ultrasound scanning of the whole breast. Ultrasound imaging takes place via an opening in a substitute breast compression paddle, rather than via application of an ultrasound transducer in direct contact with the breast compression paddle used for the x-ray imaging. Interruption between the x-ray and ultrasound imaging procedures is required for this procedure.
With respect to 3-D ultrasound imaging, Itoh, et al., developed an early ultrasound instrumentation system which provided just the outlines, that is, the shape, in three dimensions, of a breast mass. See, for example, Itoh, et al., “A Computer-Aided Three-Dimensional Display System for Ultrasonic Diagnosis of a Breast Tumor,” Ultrasonics, pp. 261-268, November, 1979. The 3-D images only included breast tumor contour outlines obtained by digitizing and computer processing image data from standard B-mode volume scans.
In 1982, J. F. Greenleaf carried out investigations of 3-D ultrasound imaging of excised breasts by digitizing and computer processing standard B-mode image data. See Greenleaf, J. F., “Three-Dimensional Imaging in Ultrasound,” J. of Med. Systems, vol. 6, no. 6, pp. 580-589, 1982.
Rotten, et al., performed 3-D breast imaging using direct contact of a standard ultrasound transducer on the uncompressed breasts of subjects lying in supine position. See, for example, Rotten, D., et al., “Three Dimensional Imaging of Solid Breast Tumors With Ultrasound: Preliminary Data and Analysis of Its Possible Contribution to the Understanding of the Standard Two-Dimensional Sonographic Images,” Ultrasound Obstet. Gynecol., vol. 1, pp. 384-390, 1991, and Rotten, D., et al., “Analysis of Normal Breast Tissue and of Solid Breast Masses Using Three-Dimensional Ultrasound Mammography,” Ultrasound Obstet. Gynecol., vol. 14, 114-124, 1999. This image data was processed by a graphic work station with three-dimensional software. The system was not designed for a precise comparison between ultrasound images and x-ray images in terms of ultrasonically imaging a breast while it is held in the same positions and under the same compression for each modality.
Hernandez, et al., in an investigation of stereoscopic visualization of 3D ultrasound breast images used a plexiglas plate to compress a breast in a craniocaudal position. A linear phased array transducer was automatically translated across the compressed breast. The ultrasound imaging was not performed by directing the ultrasound through the plexiglas, but rather, by directing the ultrasound through an opening in the plexiglas. See Hernandez, A., et al., “Stereoscopic Visualization of Three-Dimensional Ultrasonic Data Applied to Breast Tumors,” Eur. J. Ultrasound, vol. 8, no. 1, pp. 51-65, September 1998.
Various other apparatus and methods for conducting mammography are known. There are, for example, the methods and apparatus described in the following listed references: 5,640,956; 5,664,573; 5,938,613; Kelly-Fry, E., et al., “The Rationale For Ultrasound Imaging of Breasts Compressed and Positioned in the Modes Applied in X-ray Mammography,” International Breast Ultrasound School, Sep. 28-Oct. 1, 1995, pp. 126-129. This background is not intended as a representation that a thorough search of the prior art has been conducted or that no more pertinent art than that listed above exists, and no such representation should be inferred.
Though x-ray mammography is a well-accepted imaging modality for breast cancer detection, it has several shortcomings. First of all, only a through-transmission image related to integrated tissue density is obtained. Overlying diagnostic features are summed together, resulting in the possibility that important information is blurred, summed, and overlaid so it cannot be detected in the x-ray image. A further shortcoming is that the breast is imaged only up to the chest wall, but there may be abnormalities further in that are not recorded on the x-ray film. The present invention provides an additional imaging view particularly appropriate for this latter situation.